Steps to reproduce:

1. Open attached project (ShaderPerformance.zip)
2. Build 'TriangulationBug' scene for iOS
3. Deploy the generated Xcode project to a low-end device
4. Notice that the custom shader doesn't have the standard shader 'tweaks' applied, thus decreasing FPS (you can tap with two fingers to switch between custom and standard shaders and see the FPS difference)

iPad Mini 1 (iOS 6.1) and iPad 2 (iOS 8.1):
Standard shader: 30 FPS
Custom shader: 23-24 FPS

iPhone 4 (iOS 7.0):
Standar shader: ~10 FPS
Custom shader: 6-7 FPS